The colonic epithelium plays an active role in promoting colitis by shaping the tissue cytokine profile. Mus musculus

BACKGROUND & AIMS: Inflammatory Bowel Disease (IBD) is a chronic inflammatory condition driven by loss of homeostasis between the mucosal immune system, the commensal gut microbiota, and the intestinal epithelium. Our overarching goal is to understand how these components of the intestinal ecosystem cooperate to control homeostasis and to identify novel signal transduction pathways that become dysregulated in IBD. METHODS: We have applied a multi-scale systems biology approach to a mouse model of chronic colitis. We combined quantitative measures of epithelial hyperplasia and immune infiltration with multivariate analysis of inter- and intra-cellular signaling molecules in order to generate a tissue level model of the inflamed disease state. We utilized the computational model to identify signaling pathways that were dysregulated in the context of colitis and then validated model predictions by measuring the effect of small molecule pathway inhibitors on colitis. RESULTS: Our data-driven computational model identified mTOR signaling as a potential driver of inflammation and mTOR inhibition reversed the molecular, immunological, and epithelial manifestations of colitis. Inhibition of Notch signaling, which induces epithelial differentiation, had the same effect, suggesting that the epithelial proliferation/differentiation state plays a key role in maintaining homeostasis of the colon. Confirming this, we found that colonic organoids grown ex vivo showed a similar relationship between proliferation and cytokine expression, even in the absence of gut bacteria and immune cells. CONCLUSIONS: Our study provides a tissue-level systems biology perspective of murine colitis and suggests that mTOR plays a key role in regulating colonic homeostasis by controlling epithelial proliferation/differentiation state. We used microarrays to examine changes in global gene expression patterns associated with chronic inflammation induced by the T cell transfer model of Inflammatory Bowel Disease. Overall design: Rag1 knockout mice were injected with inflammation-inducing Naïve T cells or, as a negative control, regulatory T cells. Animals were sacrificed randomly after the onset of inflammation and RNA was isolated from colon tissue from the rectum to proximal-distal junction. This experiment contains expression profiles for 4 Treg-injected negative control animals, 3 severely inflamed animals and 3 moderately inflamed animals.